Check Engine 0.3.0

Check Engine tells you what's broken in a modpack, in plain English. It never changes gameplay.

Check a pack without starting the game (easiest)

1. Download CheckEngine-v0.3.0.zip below and unzip it anywhere.
2. Drag your modpack folder (for example a CurseForge instance folder) onto Check Pack.bat.
3. Read the report. It lists duplicate mods, missing dependencies, version mismatches and client-only mods that would break a server.

It uses the Java that CurseForge or the Minecraft launcher already installed, so there's nothing else to set up. Keep Check Pack.bat and checkengine-cli-0.3.0.jar in the same folder.

The checker can also explain a crash, build a server copy of a pack without the client-only mods, and compare a pack with a server to find out why players can't join:

java -jar checkengine-cli-0.3.0.jar scan <pack folder> [--server]
java -jar checkengine-cli-0.3.0.jar crash <pack folder or crash-*.txt>
java -jar checkengine-cli-0.3.0.jar serverpack <pack folder> [--out <new folder>] [--zip]
java -jar checkengine-cli-0.3.0.jar compare <pack folder> <server folder or server pack .zip>

Or use it as a mod

Put the jar for your version in the pack's mods folder:

• checkengine-neoforge-26.1-0.3.0.jar for NeoForge 26.1.2 and newer 26.1.x
• checkengine-neoforge-1.21.1-0.3.0.jar for NeoForge 1.21.1
• checkengine-forge-1.20.1-0.3.0.jar for Forge 1.20.1

Problems show on a screen before the title screen and are saved to checkengine/boot-report.txt. Server ops can run /checkengine scan to find quests, recipes and loot tables that point at mods that aren't installed, and /checkengine startup to see how long the last startup took and which mods were slowest.

What's new in 0.3.0

• NeoForge 1.21.1: Check Engine now explains why a pack won't start, right on NeoForge's error screen. It runs just before NeoForge checks dependencies, so even when the game refuses to load you see what's wrong and how to fix it, grouped ("3 mods need Create, but it isn't installed"). It uses NeoForge's own rules, so it only speaks up when NeoForge is really about to stop. Also saved to checkengine/early-report.txt.
• Clues when loading fails: if any mod breaks loading, Check Engine's warnings (duplicate mods, broken downloads...) show under the error with their fix. When the pack loads fine you just get the usual popup.
• Still one jar to install. 26.1 and Forge 1.20.1 get the same early check in a later version.

What's new in 0.2.0

• Minecraft 26.1 support (NeoForge 26.1.2+): startup check, warning screen, /checkengine scan and the join mismatch screen.
• /checkengine scan understands the newer recipe format (1.21.2+), where ingredients are plain item names.
• New /checkengine startup: how long the last startup took and the slowest mods, also saved to checkengine/startup-report.txt. The checker shows the same numbers in its report.

What's new in 0.1.4

• New logo: the Check Engine block, with its warning light and green check, also shown in the Mods menu.

What's new in 0.1.3

• Check Engine now has its icon and a link to its GitHub page in the Mods menu.
• GitHub links point at the renamed repo (Uanme37/CheckEngine).

What's new in 0.1.2

• New name: Check Engine (it was Pack Doctor; another mod already had that name). The command is now /checkengine scan and reports go to the checkengine folder.

What's new in 0.1.1

Fixes found by testing on 29 real modpacks:

• The mod now loads on any NeoForge 21.1. 0.1.0 needed 21.1.252 or newer, so it refused to start in packs like FTB Skies 2, ATM10 and Better MC.
• No more false "wrong NeoForge version" errors for mods made for 1.21 (NeoForge 1.21.1 loads them anyway).
• Respects config/fml.toml dependency overrides, and knows Monocle lets Iris run on Embeddium.
• /checkengine scan no longer warns about recipes a mod ships for optional mods you don't have (Farming for Blockheads has hundreds); they're one note now.
• scan --server gives server memory advice instead of CurseForge steps.